The present invention relates to the field of hybrid transmissions for motor vehicles comprising, on the one hand, a combustion engine for drive and, on the other hand, an electric machine.
More specifically it relates to a hybrid transmission for a motor vehicle equipped with a combustion engine and with an electric machine for drive, comprising two concentric primary shafts each bearing at least one gear for transmitting to a secondary shaft connected to the wheels of the vehicle.
Hybrid transmissions have the key benefit of offering the vehicle drivetrain two sources of power, combustion and electric, the torques supplied by which can be combined in what is known as a hybrid mode, or can be used separately, either in a “pure combustion mode” in which the electric machine supplies the drivetrain with no torque, or in a “purely electrical” mode in which the combustion engine provides the drivetrain with no torque. Other functionalities are also required, such as the possibility of starting the combustion engine from stationary or when moving, using the electric machine as a starter, or that of using the electric machine as a current generator in order to charge the batteries.
In its simplest design, a hybrid transmission as introduced hereinabove performs all the required functions on just one step-down gear ratio, i.e. without the option of enjoying several forward gears as are found in a conventional transmission.
Publication U.S. Pat. No. 5,433,282 discloses a hybrid transmission for a motor vehicle which is essentially made up of a simple epicyclic geartrain of which the three outputs, planet carrier, sun gear and annulus gear, are connected to the combustion engine, to the electric machine and to the wheels of the vehicle. The combustion engine, the electric machine and the geartrain are coaxial. A free wheel is positioned between the combustion engine and the sun gear of the gear train. It notably allows the contributions from the electric machine and from the electric machine to be combined for driving the vehicle and to have two transmission gear ratios. However, its ability to suit specific types of driving, such as typically urban driving and typically highway driving in pure electrical mode at modest speeds, and typically motorway driving at high speed, for example in pure combustion mode, are limited.